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  <div class="section" id="module-email.charset">
<span id="email-charset-representing-character-sets"></span><h1>19.1.12. <a class="reference internal" href="#module-email.charset" title="email.charset: Character Sets"><code class="xref py py-mod docutils literal notranslate"><span class="pre">email.charset</span></code></a>: Representing character sets<a class="headerlink" href="#module-email.charset" title="永久链接至标题">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/email/charset.py">Lib/email/charset.py</a></p>
<hr class="docutils" />
<p>This module is part of the legacy (<code class="docutils literal notranslate"><span class="pre">Compat32</span></code>) email API.  In the new
API only the aliases table is used.</p>
<p>The remaining text in this section is the original documentation of the module.</p>
<p>This module provides a class <a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> for representing character sets
and character set conversions in email messages, as well as a character set
registry and several convenience methods for manipulating this registry.
Instances of <a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> are used in several other modules within the
<a class="reference internal" href="email.html#module-email" title="email: Package supporting the parsing, manipulating, and generating email messages."><code class="xref py py-mod docutils literal notranslate"><span class="pre">email</span></code></a> package.</p>
<p>Import this class from the <a class="reference internal" href="#module-email.charset" title="email.charset: Character Sets"><code class="xref py py-mod docutils literal notranslate"><span class="pre">email.charset</span></code></a> module.</p>
<dl class="class">
<dt id="email.charset.Charset">
<em class="property">class </em><code class="descclassname">email.charset.</code><code class="descname">Charset</code><span class="sig-paren">(</span><em>input_charset=DEFAULT_CHARSET</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset" title="永久链接至目标">¶</a></dt>
<dd><p>Map character sets to their email properties.</p>
<p>This class provides information about the requirements imposed on email for a
specific character set.  It also provides convenience routines for converting
between character sets, given the availability of the applicable codecs.  Given
a character set, it will do its best to provide information on how to use that
character set in an email message in an RFC-compliant way.</p>
<p>Certain character sets must be encoded with quoted-printable or base64 when used
in email headers or bodies.  Certain character sets must be converted outright,
and are not allowed in email.</p>
<p>Optional <em>input_charset</em> is as described below; it is always coerced to lower
case.  After being alias normalized it is also used as a lookup into the
registry of character sets to find out the header encoding, body encoding, and
output conversion codec to be used for the character set.  For example, if
<em>input_charset</em> is <code class="docutils literal notranslate"><span class="pre">iso-8859-1</span></code>, then headers and bodies will be encoded using
quoted-printable and no output conversion codec is necessary.  If
<em>input_charset</em> is <code class="docutils literal notranslate"><span class="pre">euc-jp</span></code>, then headers will be encoded with base64, bodies
will not be encoded, but output text will be converted from the <code class="docutils literal notranslate"><span class="pre">euc-jp</span></code>
character set to the <code class="docutils literal notranslate"><span class="pre">iso-2022-jp</span></code> character set.</p>
<p><a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> instances have the following data attributes:</p>
<dl class="attribute">
<dt id="email.charset.Charset.input_charset">
<code class="descname">input_charset</code><a class="headerlink" href="#email.charset.Charset.input_charset" title="永久链接至目标">¶</a></dt>
<dd><p>The initial character set specified.  Common aliases are converted to
their <em>official</em> email names (e.g. <code class="docutils literal notranslate"><span class="pre">latin_1</span></code> is converted to
<code class="docutils literal notranslate"><span class="pre">iso-8859-1</span></code>).  Defaults to 7-bit <code class="docutils literal notranslate"><span class="pre">us-ascii</span></code>.</p>
</dd></dl>

<dl class="attribute">
<dt id="email.charset.Charset.header_encoding">
<code class="descname">header_encoding</code><a class="headerlink" href="#email.charset.Charset.header_encoding" title="永久链接至目标">¶</a></dt>
<dd><p>If the character set must be encoded before it can be used in an email
header, this attribute will be set to <code class="docutils literal notranslate"><span class="pre">Charset.QP</span></code> (for
quoted-printable), <code class="docutils literal notranslate"><span class="pre">Charset.BASE64</span></code> (for base64 encoding), or
<code class="docutils literal notranslate"><span class="pre">Charset.SHORTEST</span></code> for the shortest of QP or BASE64 encoding. Otherwise,
it will be <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>

<dl class="attribute">
<dt id="email.charset.Charset.body_encoding">
<code class="descname">body_encoding</code><a class="headerlink" href="#email.charset.Charset.body_encoding" title="永久链接至目标">¶</a></dt>
<dd><p>Same as <em>header_encoding</em>, but describes the encoding for the mail
message's body, which indeed may be different than the header encoding.
<code class="docutils literal notranslate"><span class="pre">Charset.SHORTEST</span></code> is not allowed for <em>body_encoding</em>.</p>
</dd></dl>

<dl class="attribute">
<dt id="email.charset.Charset.output_charset">
<code class="descname">output_charset</code><a class="headerlink" href="#email.charset.Charset.output_charset" title="永久链接至目标">¶</a></dt>
<dd><p>Some character sets must be converted before they can be used in email
headers or bodies.  If the <em>input_charset</em> is one of them, this attribute
will contain the name of the character set output will be converted to.
Otherwise, it will be <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>

<dl class="attribute">
<dt id="email.charset.Charset.input_codec">
<code class="descname">input_codec</code><a class="headerlink" href="#email.charset.Charset.input_codec" title="永久链接至目标">¶</a></dt>
<dd><p>The name of the Python codec used to convert the <em>input_charset</em> to
Unicode.  If no conversion codec is necessary, this attribute will be
<code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>

<dl class="attribute">
<dt id="email.charset.Charset.output_codec">
<code class="descname">output_codec</code><a class="headerlink" href="#email.charset.Charset.output_codec" title="永久链接至目标">¶</a></dt>
<dd><p>The name of the Python codec used to convert Unicode to the
<em>output_charset</em>.  If no conversion codec is necessary, this attribute
will have the same value as the <em>input_codec</em>.</p>
</dd></dl>

<p><a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> instances also have the following methods:</p>
<dl class="method">
<dt id="email.charset.Charset.get_body_encoding">
<code class="descname">get_body_encoding</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.get_body_encoding" title="永久链接至目标">¶</a></dt>
<dd><p>Return the content transfer encoding used for body encoding.</p>
<p>This is either the string <code class="docutils literal notranslate"><span class="pre">quoted-printable</span></code> or <code class="docutils literal notranslate"><span class="pre">base64</span></code> depending on
the encoding used, or it is a function, in which case you should call the
function with a single argument, the Message object being encoded.  The
function should then set the <em class="mailheader">Content-Transfer-Encoding</em>
header itself to whatever is appropriate.</p>
<p>Returns the string <code class="docutils literal notranslate"><span class="pre">quoted-printable</span></code> if <em>body_encoding</em> is <code class="docutils literal notranslate"><span class="pre">QP</span></code>,
returns the string <code class="docutils literal notranslate"><span class="pre">base64</span></code> if <em>body_encoding</em> is <code class="docutils literal notranslate"><span class="pre">BASE64</span></code>, and
returns the string <code class="docutils literal notranslate"><span class="pre">7bit</span></code> otherwise.</p>
</dd></dl>

<dl class="method">
<dt id="email.charset.Charset.get_output_charset">
<code class="descname">get_output_charset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.get_output_charset" title="永久链接至目标">¶</a></dt>
<dd><p>Return the output character set.</p>
<p>This is the <em>output_charset</em> attribute if that is not <code class="docutils literal notranslate"><span class="pre">None</span></code>, otherwise
it is <em>input_charset</em>.</p>
</dd></dl>

<dl class="method">
<dt id="email.charset.Charset.header_encode">
<code class="descname">header_encode</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.header_encode" title="永久链接至目标">¶</a></dt>
<dd><p>Header-encode the string <em>string</em>.</p>
<p>The type of encoding (base64 or quoted-printable) will be based on the
<em>header_encoding</em> attribute.</p>
</dd></dl>

<dl class="method">
<dt id="email.charset.Charset.header_encode_lines">
<code class="descname">header_encode_lines</code><span class="sig-paren">(</span><em>string</em>, <em>maxlengths</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.header_encode_lines" title="永久链接至目标">¶</a></dt>
<dd><p>Header-encode a <em>string</em> by converting it first to bytes.</p>
<p>This is similar to <a class="reference internal" href="#email.charset.Charset.header_encode" title="email.charset.Charset.header_encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">header_encode()</span></code></a> except that the string is fit
into maximum line lengths as given by the argument <em>maxlengths</em>, which
must be an iterator: each element returned from this iterator will provide
the next maximum line length.</p>
</dd></dl>

<dl class="method">
<dt id="email.charset.Charset.body_encode">
<code class="descname">body_encode</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.body_encode" title="永久链接至目标">¶</a></dt>
<dd><p>Body-encode the string <em>string</em>.</p>
<p>The type of encoding (base64 or quoted-printable) will be based on the
<em>body_encoding</em> attribute.</p>
</dd></dl>

<p>The <a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> class also provides a number of methods to support
standard operations and built-in functions.</p>
<dl class="method">
<dt id="email.charset.Charset.__str__">
<code class="descname">__str__</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.__str__" title="永久链接至目标">¶</a></dt>
<dd><p>Returns <em>input_charset</em> as a string coerced to lower
case. <a class="reference internal" href="../reference/datamodel.html#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__repr__()</span></code></a> is an alias for <a class="reference internal" href="#email.charset.Charset.__str__" title="email.charset.Charset.__str__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__str__()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="email.charset.Charset.__eq__">
<code class="descname">__eq__</code><span class="sig-paren">(</span><em>other</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.__eq__" title="永久链接至目标">¶</a></dt>
<dd><p>This method allows you to compare two <a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> instances for
equality.</p>
</dd></dl>

<dl class="method">
<dt id="email.charset.Charset.__ne__">
<code class="descname">__ne__</code><span class="sig-paren">(</span><em>other</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.Charset.__ne__" title="永久链接至目标">¶</a></dt>
<dd><p>This method allows you to compare two <a class="reference internal" href="#email.charset.Charset" title="email.charset.Charset"><code class="xref py py-class docutils literal notranslate"><span class="pre">Charset</span></code></a> instances for
inequality.</p>
</dd></dl>

</dd></dl>

<p>The <a class="reference internal" href="#module-email.charset" title="email.charset: Character Sets"><code class="xref py py-mod docutils literal notranslate"><span class="pre">email.charset</span></code></a> module also provides the following functions for adding
new entries to the global character set, alias, and codec registries:</p>
<dl class="function">
<dt id="email.charset.add_charset">
<code class="descclassname">email.charset.</code><code class="descname">add_charset</code><span class="sig-paren">(</span><em>charset</em>, <em>header_enc=None</em>, <em>body_enc=None</em>, <em>output_charset=None</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.add_charset" title="永久链接至目标">¶</a></dt>
<dd><p>Add character properties to the global registry.</p>
<p><em>charset</em> is the input character set, and must be the canonical name of a
character set.</p>
<p>Optional <em>header_enc</em> and <em>body_enc</em> is either <code class="docutils literal notranslate"><span class="pre">Charset.QP</span></code> for
quoted-printable, <code class="docutils literal notranslate"><span class="pre">Charset.BASE64</span></code> for base64 encoding,
<code class="docutils literal notranslate"><span class="pre">Charset.SHORTEST</span></code> for the shortest of quoted-printable or base64 encoding,
or <code class="docutils literal notranslate"><span class="pre">None</span></code> for no encoding.  <code class="docutils literal notranslate"><span class="pre">SHORTEST</span></code> is only valid for
<em>header_enc</em>. The default is <code class="docutils literal notranslate"><span class="pre">None</span></code> for no encoding.</p>
<p>Optional <em>output_charset</em> is the character set that the output should be in.
Conversions will proceed from input charset, to Unicode, to the output charset
when the method <code class="xref py py-meth docutils literal notranslate"><span class="pre">Charset.convert()</span></code> is called.  The default is to output in
the same character set as the input.</p>
<p>Both <em>input_charset</em> and <em>output_charset</em> must have Unicode codec entries in the
module's character set-to-codec mapping; use <a class="reference internal" href="#email.charset.add_codec" title="email.charset.add_codec"><code class="xref py py-func docutils literal notranslate"><span class="pre">add_codec()</span></code></a> to add codecs the
module does not know about.  See the <a class="reference internal" href="codecs.html#module-codecs" title="codecs: Encode and decode data and streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">codecs</span></code></a> module's documentation for
more information.</p>
<p>The global character set registry is kept in the module global dictionary
<code class="docutils literal notranslate"><span class="pre">CHARSETS</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="email.charset.add_alias">
<code class="descclassname">email.charset.</code><code class="descname">add_alias</code><span class="sig-paren">(</span><em>alias</em>, <em>canonical</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.add_alias" title="永久链接至目标">¶</a></dt>
<dd><p>Add a character set alias.  <em>alias</em> is the alias name, e.g. <code class="docutils literal notranslate"><span class="pre">latin-1</span></code>.
<em>canonical</em> is the character set's canonical name, e.g. <code class="docutils literal notranslate"><span class="pre">iso-8859-1</span></code>.</p>
<p>The global charset alias registry is kept in the module global dictionary
<code class="docutils literal notranslate"><span class="pre">ALIASES</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="email.charset.add_codec">
<code class="descclassname">email.charset.</code><code class="descname">add_codec</code><span class="sig-paren">(</span><em>charset</em>, <em>codecname</em><span class="sig-paren">)</span><a class="headerlink" href="#email.charset.add_codec" title="永久链接至目标">¶</a></dt>
<dd><p>Add a codec that map characters in the given character set to and from Unicode.</p>
<p><em>charset</em> is the canonical name of a character set. <em>codecname</em> is the name of a
Python codec, as appropriate for the second argument to the <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>'s
<a class="reference internal" href="stdtypes.html#str.encode" title="str.encode"><code class="xref py py-meth docutils literal notranslate"><span class="pre">encode()</span></code></a> method.</p>
</dd></dl>

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